This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A251795 #7 Jun 02 2025 10:31:38 %S A251795 1080,28932,724300,18577404,474547100,12140516092,310512400748, %T A251795 7942655953980,203162998830364,5196687753697688,132925430781676964, %U A251795 3400084831220237312,86970384462156604888,2224605686320053022252 %N A251795 Number of (n+1)X(2+1) 0..3 arrays with no 2X2 subblock having x11-x00 less than x10-x01. %C A251795 Column 2 of A251801 %H A251795 R. H. Hardin, <a href="/A251795/b251795.txt">Table of n, a(n) for n = 1..210</a> %F A251795 Empirical: a(n) = 30*a(n-1) -40*a(n-2) -2202*a(n-3) +7167*a(n-4) +41092*a(n-5) -170647*a(n-6) -169762*a(n-7) +1201353*a(n-8) -237196*a(n-9) -3305290*a(n-10) +2262184*a(n-11) +3737187*a(n-12) -3793360*a(n-13) -1475516*a(n-14) +2385944*a(n-15) -12352*a(n-16) -613952*a(n-17) +105792*a(n-18) +54144*a(n-19) -13824*a(n-20) %e A251795 Some solutions for n=2 %e A251795 ..2..2..2....0..1..0....0..1..2....1..3..1....0..3..2....0..0..2....2..1..3 %e A251795 ..0..1..2....1..0..3....1..0..2....2..1..3....1..0..2....2..2..3....1..3..3 %e A251795 ..0..1..1....1..3..1....1..2..3....1..2..3....1..2..1....2..2..1....1..0..1 %K A251795 nonn %O A251795 1,1 %A A251795 _R. H. Hardin_, Dec 09 2014